Japan's Emperor Akihito attended a ceremony on Sunday to mark the 30th year of his reign while calling for the country to embrace openness in a more globalised world.

The government-sponsored ceremony at the National Theatre in Tokyo was attended by Japanese Prime Minister Shinzo Abe and Empress Michiko.

"Japan has long cultivated its own culture as an island nation," the 85-year-old emperor said. "But now the world is becoming more globalised. I think it is now required for us to be more open to the outside world, to establish our own position with wisdom and to build relationships with other countries with sincerity."

Akihito's Heisei era will end when he abdicates on April 30 in favour of his elder son, 59-year-old Crown Prince Naruhito, beginning a new, as yet unnamed era.

The Emperor has cited his deteriorating health as his reason for stepping aside. While his official duties have been scaled back somewhat, he still receives visiting dignitaries, attends ceremonies and makes official visits.

Inside the palace, he also performs private rituals of Shintoism, the indigenous religion intertwined with Japan's imperial family.

In a congratulatory speech at Sunday's ceremony, Abe said the people will "never forget" how the imperial couple have "always stood by the people for 30 years."

Members of the public signed their names in registers to commemorate the emperor's 30-year reign in front of the Imperial Household Agency building on the Imperial Palace ground.

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